The present invention relates to a method and apparatus for manufacturing a color filter by discharging ink onto a substrate by an ink-jet head, a color filter and a display device manufactured by this method and apparatus, and an apparatus having the display device.
When a color filter is manufactured by discharging ink onto a substrate to color each pixel by using an ink-jet head, plural nozzles are usually used to reduce the time required for coloring. In this case, since the amount of ink discharged at a single time of electric signal (hereinafter referred to as ink discharge amount) is generally different for each nozzle, pixels colored by different nozzles have different degrees of coloring. Therefore, this causes color unevenness on the screen surface.
In view of this, the inventors of the present invention have already suggested a method of minimizing the aforementioned color unevenness, in which discharge operation is performed by the ink-jet head to be used for coloring, unevenness of the ink discharge amount of each nozzle is measured, and the ink discharge density is adjusted in accordance with the measured unevenness. For instance, as shown in FIG. 18, for a nozzle whose amount of ink discharged per single discharge operation is small, the ink discharge density is set large; whereas for a nozzle whose amount of ink discharged per single discharge operation is large, the ink discharge density is set small. In this manner, unevenness of the amount of ink discharged per single discharge operation of each nozzle is corrected by adjusting the ink discharge density of each nozzle. Accordingly, the amount of ink discharged for each pixel is made uniform. It is considered that if the ink discharged for a pixel uniformly spreads out in the pixel, a color filter without color unevenness is manufactured.
The method of adjusting the ink discharge density will be described hereinafter.
Light transmitted through a colored portion of a color filter is expressed by the following equation according to the Lambert-Beer's Law: EQU A=-Log(I/I0)=abc
A: absorbance PA1 I0: intensity of incident light PA1 I: intensity of transmitted light PA1 I/I0: transmissivity PA1 a: proportional constant PA1 b: thickness of colored portion PA1 c: density of dye in colored portion
To minimize the color unevenness, in the above equation, I/I0 must be constant for each colored portion of the color filter. "be" in the right side of the equation expresses the amount of ink discharged per unit area.
The following two points become apparent from the above equation.
(1) To eliminate the color unevenness, it is necessary to make the absorbance uniform in the colored portion of the entire surface of the filter. PA0 (2) The amount of ink per unit area and absorbance are proportional. PA0 (1) measurement error of absorbance PA0 (2) even if an accurate discharge amount at a certain moment is obtained, because of subtle changes in the ink discharge amount which is inherent to an ink-jet head, ink is not always discharged at the obtained amount, but discharged with variances.
Herein, actual discharge operation is performed by an ink-jet head to be used, the ink discharge amount of each nozzle is obtained, and the number of ink dots discharged per unit area (hereinafter referred to as ink discharge density) is determined by the following equation: EQU ink discharge density=amount of ink discharged per unit area/amount of ink discharged per single discharge operation
However, it has been discovered that the precision of the color unevenness correction of a screen surface is not always sufficient in the above example. The main causes thereof are the following two points which are classified based on the mechanism of imprecise correction.
Furthermore, these two causes are classified into the following two components if classification is based on their influence.
(1) Always constant component
An always constant component includes, for instance, measurement error generated at the time of measuring absorbance due to the fact that the absorbance of the colored portion is influenced by the absorbance of the background portion, which is the portion other than the colored portion.
(2) Random varying component
A random varying component includes, for instance, real-time variation of ink discharge amount due to changes in the state of the ink-jet head or nozzle.